Aquilops americanus

Osteological description and phylogenetic considerations of Aquilops americanus (Dinosauria, Ornithischia, Neoceratopsia) from the Early Cretaceous of North America

Aquilops americanus is a basal species of neoceratopsian that represents one of the oldest and most primitive records of this clade in North America. Its discovery, based on an exceptionally preserved partial skull from the Cloverly Formation (Early Cretaceous, Aptian–Albian) in Montana, USA, provides key evidence for the early dispersal of ceratopsians from Asia to North America during the Early Cretaceous.

The holotype specimen (OMNH 34557), corresponding to a juvenile individual, preserves a large part of the skull in lateral view, allowing a detailed characterization of its osteological morphology. The skull, barely 8.4 cm long, is proportionally elongated and low, with a curved rostroventral profile. One of the most notable characteristics of Aquilops is the pronouncedly recurved shape of the rostrum, with a downward-projecting premaxilla that gives it a hooked appearance, similar to but more subtle than that observed in more derived forms such as Protoceratops .

The rostral bone is present and fused, forming a sharp structure that contributes to the group's characteristic horny beak. Despite the basal condition of the species, Aquilops already displays an ornamented maxilla, with evidence of a row of low-crowned, ornate teeth adapted for a selective herbivorous diet. The nasal region is short, and the nasal bone arches smoothly over the skull, showing no trace of elaborate ornamentation, such as ridges or knobs. The jugal is noticeably expanded caudoventrally, beginning to outline the "jugal horn," which would become more prominent in later forms.

Although complete postcranial elements are lacking, phylogenetic comparison suggests that Aquilops was a small, facultative biped (approximately 60 cm long at life) with relatively long hindlimbs in proportion to its body size, indicative of efficient and possibly agile locomotion. The forelimbs, although shorter, were robust enough to allow occasional quadrupedal posture, consistent with those observed in other basal ceratopsians.

Phylogenetically, Aquilops americanus is placed within Neoceratopsia, in a basal position, outside of Protoceratopsidae. Its cranial morphology suggests a close relationship with Asian forms such as Liaoceratops and Archaeoceratops , which supports the hypothesis of an early ceratopsian dispersal from Asia to North America through land bridges on the eastern margin of the continent during the Early Cretaceous. This migration represents one of the first waves of faunal exchange between Asia and North America, a pattern that would be repeated in various groups of dinosaurs throughout the Mesozoic.

Approximate measurements of the Aquilops:

• 1:1 Scale Assembly Kit
• Length 585 mm
• Height 128 mm
• Width 215 mm
• Snout-tail length 600 mm
• Includes support